# subnet mask(서브넷 마스크) 비트 별 정리 #

bit  netmask Cisco mask   hosts  usable hosts  Class
/4 240.0.0.0 15.255.255.255 268435456 268435454  
 /5 248.0.0.0 7.255.255.255 134217728 134217726  
 /6 252.0.0.0 3.255.255.255  67108864 67108862  
 /7 254.0.0.0 1.255.255.255 33554432 33554430  
 /8 255.0.0.0 0.255.255.255 16777216 16777214  A Class
 /9 255.128.0.0 0.127.255.255 8388608 8388606  
 /10 255.192.0.0 0.63.255.255 4194304 4194302  
 /11 255.224.0.0 0.31.255.255 2097152 2097150  
 /12 255.240.0.0 0.15.255.255 1048576 1048574  
 /13 255.248.0.0 0.7.255.255 524288 524286  
 /14 255.252.0.0 0.3.255.255 262144 262142  
 /15 255.254.0.0 0.1.255.255 131072 131070  
 /16 255.255.0.0 0.0.255.255 65536 65534  B Class
 /17 255.255.128.0 0.0.127.255 32768 32766  
 /18 255.255.192.0 0.0.63.255 16384 16382  
 /19 255.255.224.0 0.0.31.255 8192 8190  
 /20 255.255.240.0 0.0.15.255 4096 4094  
 /21 255.255.248.0 0.0.7.255 2048 2046  
 /22 255.255.252.0 0.0.3.255 1024 1022  
 /23 255.255.254.0 0.0.1.255 512 510  
 /24 255.255.255.0 0.0.0.255 256 254  C Class
 /25 255.255.255.128 0.0.0.127 128 126  
 /26 255.255.255.192 0.0.0.63 64 62  
 /27 255.255.255.224 0.0.0.31 32 30  
 /28 255.255.255.240 0.0.0.15 16 14  
 /29 255.255.255.248 0.0.0.7 8 6  
 /30 255.255.255.252 0.0.0.3 4 2  
 /31 point to point links only
 /32 255.255.255.255  use host notaition 1 1

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